Method for preventing reduction in a reproduced output of a servo signal in a magnetic recording medium

Abstract

Servo regions are re-magnetized in the present invention. A magnetic storage device measures a first amount which is indicative of the magnitude of magnetization of a servo region, by a read head portion. The first amount may be a reproduced output, or an inverse of a gain used in an automatic gain control, etc. Servo regions are re-magnetized by a write head portion, when a servo region is detected in which a ratio of the measured first amount to an initial value of the first amount is smaller than a predetermined value, i.e., it is determined that the magnetization is reduced.

What is claimed is: 
     
       1. A method for re-magnetizing a servo region of a perpendicular magnetic recording medium in a discrete track disk type in a magnetic storage device which is provided with a magnetic head, in order to prevent reduction in a reproduced output of a servo signal recorded in the servo region, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 a first step of measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; and 
 a second step of re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the first step to an initial value of the first amount is smaller than a predetermined ratio, 
 wherein the target servo region is detected by counting a number of clocks corresponding to a time required for the magnetic head to move across a data region preceding the target servo region. 
 
     
     
       2. The method according to  claim 1 , wherein the second step includes the steps of:
 starting a servo control to position the magnetic head at a fixed position in a track width direction, when the magnetic head is positioned at a preceding servo region which precedes and is adjacent to the target servo region; 
 rotating the medium to move the magnetic head to the target servo region; 
 applying a magnetic field to the target region by the write head portion when a first gap is detected, wherein the first gap is located at a leading end of the target servo region in a rotating direction of the medium and defines a boundary between the target servo region and a preceding data region; and 
 stopping applying the magnetic field, when a second gap is detected, wherein the second gap is located at a trailing end of the target servo region in the rotating direction of the medium and defines a boundary between the target servo region and a following data region. 
 
     
     
       3. The method according to  claim 1 , wherein the target servo region is the degraded servo region which is detected at the first step. 
     
     
       4. The method according to  claim 1 , wherein the target servo region includes all the servo regions in the medium. 
     
     
       5. The method according to  claim 4 , wherein the second step is performed for all the servo regions on one track, further comprising the steps of:
 moving the magnetic head to an adjacent track; and 
 performing the second step for all the servo regions on the adjacent track. 
 
     
     
       6. The method according to  claim 4 , wherein the second step is performed for all the servo regions on a track, further comprising the steps of:
 moving the magnetic head in a track width direction by a predetermined distance less than a track width; and 
 performing the second step again for all the servo regions on the track. 
 
     
     
       7. A method for re-magnetizing a servo region of a perpendicular magnetic recording medium in a discrete track disk type in a magnetic storage device which is provided with a magnetic head, in order to prevent reduction in a reproduced output of a servo signal recorded in the servo region, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 a first step of measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; and 
 a second step of re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the first step to an initial value of the first amount is smaller than a predetermined ratio, wherein the second step includes the steps of: 
 starting a servo control to position the magnetic head at a fixed position in a track width direction, when the magnetic head is positioned at a preceding servo region which precedes and is adjacent to the target servo region; 
 rotating the medium to move the magnetic head to the target servo region; 
 applying a magnetic field to the target region by the write head portion when a first gap is detected, wherein the first gap is located at a leading end of the target servo region in a rotating direction of the medium and defines a boundary between the target servo region and a preceding data region; and 
 stopping applying the magnetic field, when a second gap is detected, wherein the second gap is located at a trailing end of the target servo region in the rotating direction of the medium and defines a boundary between the target servo region and a following data region, 
 wherein the first and second gaps are detected by counting a number of clocks corresponding to a time required for the magnetic head to move across the data region and the servo region, respectively. 
 
     
     
       8. A method for re-magnetizing a servo region of a perpendicular magnetic recording medium in a discrete track disk type in a magnetic storage device which is provided with a magnetic head, in order to prevent reduction in a reproduced output of a servo signal recorded in the servo region, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 a first step of measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; and 
 a second step of re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the first step to an initial value of the first amount is smaller than a predetermined ratio, wherein the second step includes the steps of: 
 starting a servo control to position the magnetic head at a fixed position in a track width direction, when the magnetic head is positioned at a preceding servo region which precedes and is adjacent to the target servo region; 
 rotating the medium to move the magnetic head to the target servo region; 
 applying a magnetic field to the target region by the write head portion when a first gap is detected, wherein the first gap is located at a leading end of the target servo region in a rotating direction of the medium and defines a boundary between the target servo region and a preceding data region; and 
 stopping applying the magnetic field, when a second gap is detected, wherein the second gap is located at a trailing end of the target servo region in the rotating direction of the medium and defines a boundary between the target servo region and a following data region, 
 wherein the first and second gaps are detected by reading signals indicative of existence of the gap by the read head portion, wherein each signal is recorded at a location adjacent to the servo region in the preceding and in the following data regions, respectively. 
 
     
     
       9. A method for re-magnetizing a servo region of a perpendicular magnetic recording medium in a discrete track disk type in a magnetic storage device which is provided with a magnetic head, in order to prevent reduction in a reproduced output of a servo signal recorded in the servo region, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 a first step of measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; 
 a second step of re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the first step to an initial value of the first amount is smaller than a predetermined ratio; and 
 a third step of measuring the first amount after the second step was performed, wherein the measured first amount will be used for the initial value thereafter. 
 
     
     
       10. The method according to  claim 1 , further comprising:
 a fourth step of saving a date and a time when the re-magnetization was performed, for each servo region, 
 wherein the first step and the second step are performed again after a predetermined time has passed since the time of the date. 
 
     
     
       11. The method according to  claim 1 , wherein the predetermined ratio is in a range of 0.85 to 0.95. 
     
     
       12. The method according to  claim 1 , wherein the first amount is the reproduced output of the servo region. 
     
     
       13. The method according to  claim 1 , wherein the first amount is an inverse of a gain used in an automatic gain control. 
     
     
       14. The method according to  claim 1 , wherein the first step and the second step are performed when no command is received from a central processing unit in a host to read or write the data signal. 
     
     
       15. A method for re-magnetizing a servo region of a perpendicular magnetic recording medium in a discrete track disk type in a magnetic storage device which is provided with a magnetic head, in order to prevent reduction in a reproduced output of a servo signal recorded in the servo region, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 (a) measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; 
 (b) re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the step (a) to an initial value of the first amount is smaller than a predetermined ratio; 
 (c) halting the step (b) when a command is received from a central processing unit in a host to read or write the data signal during the step (b), and saving a track number and a sector number of the servo region which was being re-magnetized when the command was received; and 
 (d) reading the track number and the sector number saved at the step (c) when a predetermined time has passed since the command was received, and resuming the step (b) from the servo region which has the read sector number and the read track number. 
 
     
     
       16. A read only memory in which a program is recorded to operate a computer to perform the method according to  claim 1 . 
     
     
       17. A magnetic storage device comprising:
 the perpendicular magnetic recording medium in the discrete track disk type; 
 the magnetic head; and 
 a central processing unit to read the program from the read only memory according to  claim 16 , and to perform the first step and the second step by the write head portion and the read head portion, thereby preventing reduction in the reproduced output of the servo signal recorded in the servo region of the perpendicular magnetic recording medium. 
 
     
     
       18. A method for re-magnetizing a servo region of a magnetic recording medium which is provided with a magnetic head having a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 applying a magnetic field to a target servo region by the write head portion when a first gap is detected, wherein the first gap is located at a leading end of the target servo region in a rotating direction of the medium and defines a boundary between the target servo region and a preceding data region; and 
 stopping applying the magnetic field, when a second gap is detected, wherein the second gap is located at a trailing end of the target servo region in the rotating direction of the medium and defines a boundary between the target servo region and a following data region, 
 wherein the first and second gaps are detected by counting a number of clocks corresponding to a time required for the magnetic head to move across the data region and the servo region, respectively. 
 
     
     
       19. A method for re-magnetizing a servo region of a magnetic recording medium which is provided with a magnetic head having a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 applying a magnetic field to a target servo region by the write head portion when a first gap is detected, wherein the first gap is located at a leading end of the target servo region in a rotating direction of the medium and defines a boundary between the target servo region and a preceding data region; and 
 stopping applying the magnetic field, when a second gap is detected, wherein the second gap is located at a trailing end of the target servo region in the rotating direction of the medium and defines a boundary between the target servo region and a following data region, 
 wherein the first and second gaps are detected by reading signals indicative of existence of the gap by the read head portion, wherein each signal is recorded at a location adjacent to the servo region in the preceding and in the following data regions, respectively. 
 
     
     
       20. A method for re-magnetizing a servo region of a magnetic recording medium which is provided with a magnetic head, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 a first step of measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; 
 a second step of re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the first step to an initial value of the first amount is smaller than a predetermined ratio; and 
 a third step of measuring the first amount after the second step was performed, wherein the measured first amount will be used for the initial value thereafter. 
 
     
     
       21. A method for re-magnetizing a servo region of a magnetic recording medium which is provided with a magnetic head, wherein the magnetic head has a write head portion to record a data signal and a read head portion to read the data signal, the method comprising:
 (a) measuring a first amount which is indicative of a magnitude of magnetization in the servo region, by the read head portion; 
 (b) re-magnetizing at least one of the servo regions as a target servo region by the write head portion, when a degraded servo region is detected in which a ratio of the first amount measured at the step (a) to an initial value of the first amount is smaller than a predetermined ratio; and 
 (c) halting the step (b) when a command is received from a central processing unit in a host to read or write the data signal during the step (b), and saving a track number and a sector number of the servo region which was being re-magnetized when the command was received. 
 
     
     
       22. The method of  claim 21  further comprising:
 (d) reading the track number and the sector number saved at the step (c) when a predetermined time has passed since the command was received, and resuming the step (b) from the servo region which has the read sector number and the read track number.